Bearings in wind turbines are usually lubricated with grease, however, such grease lubrication involves relatively short service intervals for replenishing the grease and after a certain amount of time the grease has to be exchanged.
From WO 03/078870 A1 a gear unit for a wind turbine is known comprising a planet gear where lubrication is effected by a stationary pump feeding oil through stationary oil lines. EP 1 431 575 A2 is another example for a planet gear where oil is supplied by channels which are connected to a pump.
Other bearings for wind turbines are known which are disposed in a gearbox with an oil sump and the bearing is lubricated during rotation.
All these bearings for wind turbines require a complicated lubrication system because it has to be ensured that all areas of the bearing receive sufficient oil. Due to the increasing size of such bearings, special attention has to be given to the top region of the bearing in order to supply the needed amount of oil for lubrication.